In large scale manufacturing and assembly plants, such as those used in automobile manufacturing, hundreds of machines and their machine operators may work simultaneously. In a large production environment, the production line may include miles of conveyors. The plant itself may be millions of square feet. An increase in the precision of production timing and/or control may provide better resource allocation. Accordingly, processes and controls that keep the line moving may increase production and reduce expenses.
A plant's hours of operation may include three shifts. For example, at the beginning of the day, oftentimes there is work in progress left at the end of the previous shift. Work in progress includes but is not limited to units of production, pallets, carriers, product, parts and units of production and items of production. Throughput is the number of items produced or processed during a period of time.
Along the many sections of conveyor of a large plant, there may be a plurality of sections that are empty or full. A buffer is storage area such as a conveyor, transport (i.e., forklift, cart, truck, etc.), silo between stations (either manual or automatic), or simply a place on the floor. A buffer generally can hold parts in excess of standard in-process stock, and provides capability to cover potential production losses due to downtime, lost time, and quality issues. Here, standard in-process stock means the minimum number of parts on the line required to maintain continuous flow of products through the manufacturing line at the intended line speed.
In a single shift, a machine station at an automotive plant may process up to hundreds and even thousands of products. The conveyor belt may move at several feet per second. The line can move fast and operations can be complex. In a single automotive assembly line, there may be hundreds of machine stations and zero or more machine operators per station. Stopping a unit of production for staging or choosing to let the unit of production move on a conveyor belt under the continuous flow model can cause problems. Since stopping a unit of production from moving takes typically 0.5 seconds over takt time, units of production can become bottlenecked quickly and downstream machines can be starved. Over the course of processing 1000 units of production per shift an ad hoc and manual approach to shutting down machines, stations, or buffers may mean substantial losses in time and resources.
A primary goal of operating a production system is to maximize throughput by keeping the system running as much as possible. Competing with this goal is the need to periodically shut down parts of the system to allow for maintenance, working training, team meetings, or other tasks. Facilitating such stoppages, buffers can separate production systems into subsystems, allowing downstream and upstream subsystems to continue to operate for a while when a subsystem is temporarily shut down. In addition, buffers may themselves be considered as subsystems whose states may be monitored and managed. The separation of a production system into such subsystems can create dynamic and temporal dependencies between subsystems and make it difficult to optimize the timing and duration of shutdowns to achieve a set of goals while minimizing lost throughput.
Processes and systems that improve the ability to perform, with minimal throughput loss and in a timely manner, tasks requiring subsystems be shut down such as preventive maintenance, training, team meetings, and calibration accordingly may increase overall production system effectiveness and may also enable subsystems to coordinate their end-of-day shutdown in a manner that can accommodate maintenance requirements while minimizing the associated throughput losses.